pH adjustment of local anesthetic solutions with sodium bicarbonate: laboratory evaluation of alkalinization and precipitation.

pH adjustment of several commonly administered local anesthetic solutions was evaluated in the laboratory. The pH achieved after the addition of sodium bicarbonate and the onset of precipitation for alkalinized solutions were recorded. Solutions of 2-chloroprocaine and lidocaine readily alkalinized to near physiological pH without precipitation. Mepivacaine solutions exhibited a tendency for delayed precipitation (18-20-minute latency for 1.5% mepivacaine) above neutral pH. Bupivacaine and etidocaine solutions precipitated after the addition of small amounts of sodium bicarbonate and could not be alkalinized to physiologic pH. Two commercially available sodium bicarbonate preparations, 4% (wt/vol) and 8.4% (wt/vol), were compared and produced similar pH changes and precipitation behavior. The data obtained for pH and time to precipitation for local anesthetic solutions alkalinized with sodium bicarbonate may be useful for practical application in the clinical setting.